Systems and methods to selectively connect antennas to receive and backscatter radio frequency signals

ABSTRACT

Systems and methods to selectively attach and control antennas via diodes. In one embodiment, a system includes: a reader having a plurality of reader antennas of different polarizations to transmit radio frequency signals; and at least one radio frequency device. The radio frequency device includes: a plurality of tag antennas of different polarizations; a plurality of diodes coupled to the plurality of tag antennas respectively; a receiver coupled to the plurality of diodes to receive the radio frequency signals from the tag antennas when the diodes are forward biased; and a set of one or more current controllers coupled to the plurality of diodes. In a receiving mode the controllers selectively forward bias the diodes to receive the signals from the reader. In a transmitting mode the controllers selectively change the state of the tag antennas to transmit data via backscattering the radio frequency signals.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 13/780,533, filed Feb. 28, 2013 and entitled“Systems and Methods to Selectively Connect Antennas to Receive andBackscatter Radio Frequency”, which is a continuation application ofU.S. patent application Ser. No. 13/301,565, filed Nov. 21, 2011 andissued as U.S. Pat. No. 8,405,509 on Mar. 26, 2013, which is acontinuation application of U.S. patent application Ser. No. 12/132,594,filed Jun. 3, 2008 and issued as U.S. Pat. No. 8,115,637 on Feb. 14,2012, the entire disclosures of which applications are incorporatedherein by reference.

FIELD OF THE TECHNOLOGY

At least some embodiments disclosed herein relate to coupling ofantennas to a communication system, such as a radio frequencyidentification (RFID) system.

BACKGROUND

A typical radio frequency identification (RFID) tag has a memoryconfigured to store data. The data stored in the tag memory typicallyincludes data that uniquely identifies the tag among a plurality of RFIDtags. An RFID reader can be used to communicate with the tag over aradio link. Thus, the identity of the tag and the object labeled by thetag can be determined by the RFID reader in an automated process.

In a typical RFID system, an RFID reader is configured to interrogatethe tags via radio frequency electromagnetic waves. The RFID readerbroadcasts commands using a beam of electromagnetic wave. In response tothe interrogation signals from the reader, the RFID tag may be selectedto produce a radio frequency response signal.

An RFID tag may be a passive tag, a semi-passive tag, or an active tag,depending on the power source of the RFID tag and the way a responsesignal is produced.

A passive tag does not have an internal battery or power source. Apassive RFID tag operates using the power drawn from the interrogatingelectromagnetic wave. A passive tag provides the response through themodulation of backscattering of the interrogating electromagnetic wave.

A semi-active tag has an internal battery or power source. A semi-activeRFID tag operates using the power drawn from the internal battery orpower source. A semi-active provides the response through the modulationof the backscattering of the interrogating electromagnetic wave.

An active tag that has an internal battery or power source, using whicha separate transmission signal is generated to provide the response. Theresponse signal is generated independent from the interrogatingelectromagnetic wave.

Radio frequency identification (RFID) tags are used in a variety ofapplications, such as tagging vehicles on toll roads, tagging shippingcontainers, quality control on assembly line conveyor belts, andmonitoring tactical military equipment maneuvers, etc.

There are various ways to configure and use antennas in a. RFID system.For example, Tuttle disclosed in U.S. Pat. No. 5,572,226 an RFID systemin which a plurality of antennas arranged in a two dimensional plane arecombined to represent a nearly spherical antenna pattern in threedimensions. Tuttle disclosed in U.S. Pat. No. 6,574,454 an RFID systemin which an antenna is coupled to a receiver via a Schottky diode. Thedisclosures of the above mentioned U.S. Patents by Tuttle areincorporated herein by reference.

SUMMARY OF THE DESCRIPTION

Systems and methods to selectively attach and control antennas viadiodes and current sources are described herein. Some embodiments aresummarized in this section.

In one embodiment, a system includes: an RFID reader having a pluralityof reader antennas of different polarizations to transmit radiofrequency signals; and at least one RFID tag. The RFID tag includes: aplurality of tag antennas of different polarizations; a plurality ofdiodes coupled to the plurality of tag antennas respectively; a receivercoupled to the plurality of diodes to receive the radio frequencysignals from the tag antennas when the diodes are forward biased; and aset of one or more current controllers coupled to the plurality ofdiodes. In a receiving mode the controllers selectively forward bias thediodes to receive the signals from the RFID reader. In a transmittingmode the controllers selectively change the state of the tag antennas totransmit data via backscattering the radio frequency signals.

The disclosure includes methods and apparatuses which perform thesemethods, including data processing systems which perform these methods,and computer readable media containing instructions which when executedon data processing systems cause the systems to perform these methods.

Other features will be apparent from the accompanying drawings and fromthe detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments are illustrated by way of example and not limitation inthe figures of the accompanying drawings in which like referencesindicate similar elements.

FIG. 1 shows a radio frequency identification system according to oneembodiment.

FIG. 2 shows an antenna connection system according to one embodiment.

FIG. 3 illustrates an example to connect an antenna according to oneembodiment.

FIG. 4 illustrates an example to selectively use a set of antennasaccording to one embodiment.

FIG. 5 illustrates an example to connect a plurality of antennas inparallel according to one embodiment.

FIG. 6 illustrates an example to connect a plurality of antennas one ata time according to one embodiment.

FIG. 7 shows an example to arrange multiple antennas for connectionaccording to one embodiment.

FIG. 8 illustrates an example to selectively connect an RFID circuit tofeed points of a patch antenna system according to one embodiment.

FIG. 9 illustrates a method implemented in a radio frequency deviceaccording to one embodiment.

DETAILED DESCRIPTION

The following description and drawings are illustrative and are not tobe construed as limiting. Numerous specific details are described toprovide a thorough understanding. However, in certain instances, wellknown or conventional details are not described in order to avoidobscuring the description. References to one or an embodiment in thepresent disclosure are not necessarily references to the sameembodiment; and, such references mean at least one.

In at least one embodiment of the disclosure, an antenna of a radiofrequency device is coupled to a receiver via a diode. When the diode isforward biased using a current source, the impedance of the diode forthe antenna signal is reduced and thus allow the antenna signal to enterthe receiver. When the diode is not forward biased, the impedance of thediode for the antenna signal is high and thus prevents the antennasignal from entering the receiver. Thus, the diode functions as a switchbetween the antenna and the receiver.

In one embodiment, the same current source that is used to selectivelybias the diode is also used to change the state of antenna to modulatebackscatter by the antenna. During a transmission mode, the impedance ofthe current source is controlled to change the state of the antenna fordata transmission via backscattering.

Using the same current source for both antenna selection and datatransmission can reduce cost and complexity, and improve systemreliability, especially if the diode is placed near the feed point ofthe antenna.

FIG. 1 shows a radio frequency identification (RFID) system according toone embodiment. In FIG. 1, the system (100) includes a data processingsystem (112) coupled to an RFID reader circuit (110). The dataprocessing system (112) may include a general purpose computer, or aspecial purpose computer, or a set of computers coupled to the readercircuit (112) via a data communication network, such as a local areanetwork, Internet, etc. The reader circuit (110), or a combination ofthe reader circuit (110) and the data processing system (112), may alsobe referred to as an interrogator or reader.

In FIG. 1, the reader has a plurality of antennas (e.g., 114 and 116).In one embodiment, the plurality of antennas have differentpolarizations. The reader selectively couples its transmitter to one ofthe antennas to transmit signals via the selected antenna. Thus, thereader can transmit the signals in different combinations ofpolarizations.

In FIG. 1, the reader circuit (110) communicates with a representativeRFID tag (101), which may be one of a plurality of RFID tags that arewithin the communication range of the RFID system. The reader circuit(110) provides a carrier signal to power the antenna (114) and/or theantenna (116) to send a beam of interrogating electromagnetic wave tothe RFID tag. Commands to the RFID tags are modulated on the carriersignal.

The RFID tag (101) includes a plurality of tag antennas (e.g., 104, 106)to receive the interrogating electromagnetic wave. In one embodiment,the tag antennas (e.g., 104, 106) also have different polarizations. TheRFID system uses signals of different polarizations to improve signalreception and/or to determine the orientation of the RFID tag. Inanother embodiment, the reader transmits using one antenna configuredfor one polarization; and the RFID tag is configured to have multipleantennas of different polarizations to achieve signal reception that issubstantially independent from the orientation of the RFID tag.

In one embodiment, the RFID tag (101) includes an RFID circuit (e.g.,102) to process commands received from the RFID reader. Based on thecommands, the RFID tag (101) can be selectively silenced (e.g., beingplaced in a mode to reduce interrogating electromagnetic wavebackscattered from the tag, or not to actively transmit any signalsusing its internal power source), or be instructed to produce aresponse.

In one embodiment, the interrogation signal from the reader circuit(110) is received by the tag antenna (104 and/or 106) and passed to theRFID circuit (102) for processing. If the interrogation signal triggersa response, the RFID circuit (102) uses its tag antenna (104 and/or 106)to send to the reader circuit (19) a response, such as tagidentification information or other data stored in the memory of the tag(101).

The reader circuit (110) passes the data obtained from the RFID tags tothe data processing system (112), which performs any suitable function.For example, based on the data received from the RFID tag (101), thedata processing system (112) may allow access to a building or parkinggarage, note the entrance of an employee to a work location, direct aparcel identified by the RFID tag down a particular conveyor system, orconduct inventory of products in a shopping cart for purposes ofcheckout and payment.

In one embodiment, the tag antennas (104 and 106) are coupled to theRFID circuit (102) via diodes. Current sources used to bias the diodesare also used to change the backscatter state of the antennas (104 and106) for transmission of data via backscattering the interrogatingsignals transmitted from the reader antennas (114 and/or 116).

FIG. 2 shows an antenna connection system according to one embodiment.In FIG. 2, the antenna (120) is coupled to the receiver (124) via acapacitor (121) and a diode (122). When the diode (122) is forwardbiased, the impedance of the diode (122) for the Alternating Current(AC) signal from the antenna (120) is reduced, providing a path to allowthe signals received at the antenna (120) to enter the receiver (124).When the diode (122) is not forward biased (or reverse biased), theimpedance of the diode (122) is high to prevent the antenna signal fromentering the receiver (124). Inductor (136) provides a DC current pathwhen the current source (126) is ON, while presenting a high impedanceto the AC signal from the antenna; and the capacitor (121) blocks the DCcurrent from entering the antenna (120).

In FIG. 2, a controllable current path, such as the controllable currentsource (126), is coupled between the diode (122) and the ground toselectively bias the diode (122) based on the voltage applied at thecontrol point (128). For example, when a first control voltage isapplied to the control point (128), the diode (122) is forward biasedvia a Direct Current (DC) provided by the current source (126); when asecond voltage is applied to the control point (128), the DC biascurrent supplied by the current source to the diode (122) is reduced orstopped. Thus, the current source (126) can be selectively controlled tocouple the AC signals from the antenna (120) to the receiver (124) or toisolate the antenna signals from the receiver (124).

In FIG. 2, the impedance of the current source (126) is also adjustableby the voltage applied at the control point (128). When the impedance ofthe current source is high, the antenna (120) is in a reflective state;when the impedance of the current source is low, the antenna (120) is inan absorptive state. Thus, changing the impedance of the current sourcevia the control voltage can also be used to modulate the interrogationsignal backscattered by the tag antenna (120). The backscatteredinterrogation signal can be modulated to transmit data. A reader systemcan send an interrogating electromagnetic wave and determine the tagtransmitted data from the amplitude modulated wave backscattered fromthe tag antenna.

In one embodiment, the current source (126) is implemented using atransistor, as illustrated in FIG. 3. In FIG. 3, the antenna (130) iscoupled to the receiver (142) via a capacitor (134) and a diode (132).An inductive element (136), a capacitive element (134) and a transistor(138) are used to selectively bias the diode (132). The gate of thetransistor (138) can be used to control the bias current and be used toturn the transistor on and off for modulating the backscatter by the tagantenna (130) for data transmission.

In FIG. 3, when the system is in a receiving mode, the multiplexer (140)selects the antenna selection signal, which causes the transistor (138)to selectively provide a forward bias current to the diode (132). Forexample, when the antenna selection is at a first voltage, the diode isforward biased to switch on the connection between the antenna (130) andthe receiver (142); when the antenna selection is at a second voltage,the diode is not sufficiently forward biased and thus switches off theconnection between the antenna (130) and the receiver (142). When thediode (132) is forward biased, the antenna signal is provided to thereceiver (142). When the diode (132) is not forward biased, the antennasignal is not provided from the antenna (130) to the receiver (142).

In one embodiment, when the antenna signal is not provided from theantenna to the receiver (142), the energy from the antenna is redirectedto charge a battery cell of the system.

In one embodiment, when the system is in a transmitting mode, the datasignal provided to the multiplexer (140) changes between a third voltageand a forth voltage, which may be the same as or different from thefirst and second voltages of the antenna selection signal that is usedto control the bias current of the diode (132). When the third voltageis applied to the gate of the transistor (138), the impedance betweenthe source and drain of the transistor (138) is low (e.g., thetransistor is switched on); and thus, the antenna (130) is in anabortive state and the signal backscattered from the antenna (130) has alow amplitude. When the forth voltage is applied to the gate of thetransistor (138), the impedance between the source and drain of thetransistor (138) is high (e.g., the transistor is switched off); andthus, the antenna (130) is in a reflective state and the signalbackscattered from the antenna (130) has a high amplitude.

Thus, the same transistor (138) is used for antenna selection in areceiving mode and used for data transmission in a transmitting mode.

Although FIG. 3 illustrates an example to use a multiplexer to combinethe antenna selection signal and the data signal to generate the controlvoltage for the gate of the transistor, other types of logic circuit oranalog circuit can also be used to generate the control signal for thegate of the transistor.

FIG. 4 illustrates an example to selectively use a set of antennasaccording to one embodiment. In one embodiment, a RFID tag has aplurality of antennas (162, 164, . . . , 166), which are coupled to thereceiver (148) through the DC blocking capacitors (161, 163, . . . ,165) and the diodes (156, 158, . . . , 160) respectively. The RFID tagincludes at least a memory (not shown in FIG. 4) coupled to a receiver.The memory stores identification data of the RFID device. Afterreceiving a request or command using the receiver, the identificationdata is transmitted via signals backscattered by one or more of theantennas (162, 164, . . . , 166).

The antenna connection system can also be used in other types of radiofrequency devices, which may not have a memory to identify the device.For example, the radio frequency device may be used to collect andreport information, such as temperature, etc.

In FIG. 4, the inductors (155, 157, . . . , 159), the capacitors (161,163, . . . , 165) and the controllable current sources (150, 152, . . ., 154) are used to selectively forward bias the corresponding diodes(156, 158, . . . , 160) in the receiving mode. In one embodiment, thecontrol voltages (V_(A), V_(B), . . . , V_(X)) for the current sources(150, 152, . . . , 154) are generated and applied by the radio frequencydevice (e.g., an RFID tag).

For example, the antennas (162, 164, . . . , 166) can be configured tohave different polarizations and selectively used to optimize signalreception. For example, the antennas (162, 164, . . . , 166) can be usedin parallel or sequentially to achieve a nearly spherical antennapattern in three dimensions, while the antennas (162, 164, . . . , 166)are arranged in a two dimensional plane (e.g., as a patch antennasystem). For example, the polarizations of the antennas can be alignedwith certain axes of an object to which the RFID tag is attached; andthrough interrogating the RFID using signals of different polarization,the orientation of the object can be determined or estimated.

In FIG. 4, one or more of the controllable current sources (150, 152, .. . , 154) are used to selectively modulate the backscatter by thecorresponding antennas according to the data to be transmitted. Theimpedance of the controllable current sources (150, 152, . . . , 154)can be changed to selectively ground the corresponding antennas totransmit the data. The data can be transmitted by alternating theantennas between a state of absorption and a state of reflection torepresent the bit values of the transmitted data.

FIG. 5 illustrates an example to connect a plurality of antennas inparallel according to one embodiment. In FIG. 5, a single current source(178) is used to control the antennas (171, 173, . . . , 175) inparallel. An inductor (267), DC blocking capacitors (261, 263, . . . ,265) and a current source (178) selectively bias the diodes (172, 174, .. . , 176) in parallel.

In the receiving mode, the current source (178) can be controlled by theRFID circuit (170) to forward bias the diodes (172, 174, . . . , 176) toconnect the antenna signals to the RFID circuit (170), or to stop theforward DC bias current for the diodes (172, 174, . . . , 176) todisconnect the antenna signals from the receiver of the RFID circuit(170).

In the transmitting mode, the current source (178) is controlled toselectively ground the antennas (171, 173, . . . , 175) to modulatebackscattering of the interrogation signals.

In one embodiment, the RFID device has one or more chargeable batterycells. When the diodes (172, 174, . . . , 176) are not forward biased toreceive signals, the antennas are used to trickle charge of the batterycells.

FIG. 6 illustrates an example to connect a plurality of antennas one ata time according to one embodiment. In FIG. 6, the controller (182)connects the control signal to the gates of the transistors (192, 194, .. . , 196) one at a time. The transistors (192, 194, . . . , 196) areconnected to the antenna diodes (184, 186, . . . , 188) respectively tocontrol the use of the corresponding antennas (181, 183, . . . , 185).

In one embodiment, when the gate of a transistor (e.g., 194 or 196) isnot connected to the control signal V_(control), the transistor (e.g.,194 or 196), the corresponding inductor (e.g., 293 or 295) and DCblocking capacitor (e.g., 283 or 285) do not forward bias thecorresponding diode (e.g., 186 or 188); and the signal from thecorresponding antenna (e.g., 183) is isolated from the receiver of theRFID circuit (180). When the gate of a transistor (e.g., 192) isconnected to the control signal V_(control), the transistor (e.g., 192),the corresponding inductor (e.g., 291) and DC blocking capacitor (e.g.,281) forward bias the corresponding diode (e.g., 184) during thereceiving mode; and the gate of the transistor (e.g., 192) isselectively turned on or off to module antenna backscattering for datatransmission.

In another embodiment, when the gate of the transistor (e.g., 196) isnot connected to the control signal V_(control), the transistor (e.g.,196) is turned off to stop the forward bias current for thecorresponding diode (e.g., 188) in the receiving mode, and turned on toground the corresponding antenna (e.g., 185) to reduce backscattering bythe corresponding antenna (e.g., 181).

FIG. 7 shows an example to arrange multiple antennas for connectionaccording to one embodiment. In FIG. 7, the antenna system (200)includes dipole antennas (204 and 206) and a loop antenna (208). Thedipole antennas are arranged to be perpendicular to each other, orapproximately perpendicular to each other. The loop antenna is arrangedto have at least an axis perpendicular to at least one of the dipoleantennas (204 and 206). Alternatively, a circular loop antenna can beused.

Since a radio frequency voltage will produce a toroidal shapedelectromagnetic field centered about a dipole antenna, the antennaconfiguration illustrated in FIG. 7 will effectively achieve a nearlyspherical electromagnetic filed pattern when combined by switching themone at a time. When the combined coverage is approximately spherical,the signal transmission and/or reception are substantially independentfrom the orientation of the RFID device.

Although FIG. 7 illustrates a particular combination of dipole antennas(204 and 206) and a loop antenna (208), other combination of twodimensional antennas arranged on a plane can also be used. Furtherdetails in using a set of two dimensional antennas to obtain a nearlyspherical antenna pattern in three dimensions can be found in U.S. Pat.No. 5,572,226, the disclosure of which is incorporated herein byreference.

In one embodiment, an antenna system having antennas with differentpolarizations as illustrated in FIG. 7 are connected to and controlledby an RFID device via diodes and one or more controllable current paths.The current paths can be controlled to selectively forward bias thediodes for antenna selection and to selectively ground the antennas formodulating signals backscattered by the antennas.

FIG. 8 illustrates an example to selectively connect an RFID circuit tofeed points of a patch antenna system according to one embodiment. InFIG. 8, the patch antenna system includes a ground plane or groundelement (204) and a conductive patch (200) (e.g., copper, aluminum,etc.), separated by a dielectric layer (202) (e.g., air, silicon,plastic, etc.). The patch antenna system is arranged generally on aplanar surface.

In FIG. 8, the conductive patch (200) defines a plurality of antennasand includes a plurality of feed points (e.g., 208, 206, and 210) of theantennas. The feed points may be located in the interior of theconductive patch, or on the periphery of the patch. Using different feedpoints alone or in combination can optimize the antenna reception forelectromagnetic wave of different polarizations.

In one embodiment, the diodes and/or the corresponding controllablecurrent paths are arranged at the vicinity of the corresponding feedpoints. For example, the diodes can be implemented using discreteelements and placed near the feed points. For example, the patch antennacan be formed on or attached to a printed circuit board; and the diodescan be mounted to the printed circuit board near the feed points in theplane of the printed circuit board.

Alternatively, the diodes and the corresponding controllable currentpaths can be integrated on a same semiconductor substrate (e.g.,silicon) as the RFID circuit.

FIG. 9 illustrates a method implemented in a radio frequency deviceaccording to one embodiment. In FIG. 9, when the device is in areceiving mode, the direct current in a circuit path is adjusted (220)to selectively forward bias a diode that is coupled between an antennaand a receiver. For example, the control voltage of a current source isadjusted to change the current in the circuit path of the current sourceto adjust the DC bias current and/or voltage in the diode. In oneembodiment, the current source is a provided via a transistor. The gateof the transistor is used to control the current in the circuit pathbetween the source and drain of the transistor.

When the device is in a transmitting mode, the impedance of the circuitpath is adjusted to change the state of the antenna for backscattering.For example, the impedance in the circuit path between the source anddrain of the transistor can be controlled to selectively place theantenna in an absorptive mode or in a reflective mode and thus modulatethe signals backscattered by the antenna. Modulation of thebackscattered signal is used to indicate the transmitted data.

In this description, various functions and operations may be describedas being performed by or caused by software code to simplifydescription. However, those skilled in the art will recognize what ismeant by such expressions is that the functions result from execution ofthe code by a processor, such as a microprocessor. Alternatively, or incombination, the functions and operations can be implemented usingspecial purpose circuitry, with or without software instructions, suchas using Application-Specific Integrated Circuit (ASIC) orField-Programmable Gate Array (FPGA). Embodiments can be implementedusing hardwired circuitry without software instructions, or incombination with software instructions. Thus, the techniques are limitedneither to any specific combination of hardware circuitry and software,nor to any particular source for the instructions executed by the dataprocessing system.

While some embodiments can be implemented in fully functioning computersand computer systems, various embodiments are capable of beingdistributed as a computing product in a variety of forms and are capableof being applied regardless of the particular type of machine orcomputer-readable media used to actually effect the distribution.

At least some aspects disclosed can be embodied, at least in part, insoftware. That is, the techniques may be carried out in a computersystem or other data processing system in response to its processor,such as a microprocessor, executing sequences of instructions containedin a memory, such as ROM, volatile RAM, non-volatile memory, cache or aremote storage device.

Routines executed to implement the embodiments may be implemented aspart of an operating system or a specific application, component,program, object, module or sequence of instructions referred to as“computer programs.” The computer programs typically comprise one ormore instructions set at various times in various memory and storagedevices in a computer, and that, when read and executed by one or moreprocessors in a computer, cause the computer to perform operationsnecessary to execute elements involving the various aspects.

A machine readable medium can be used to store software and data whichwhen executed by a data processing system causes the system to performvarious methods. The executable software and data may be stored invarious places including for example ROM, volatile RAM, non-volatilememory and/or cache. Portions of this software and/or data may be storedin any one of these storage devices. Further, the data and instructionscan be obtained from centralized servers or peer to peer networks.Different portions of the data and instructions can be obtained fromdifferent centralized servers and/or peer to peer networks at differenttimes and in different communication sessions or in a same communicationsession. The data and instructions can be obtained in entirety prior tothe execution of the applications. Alternatively, portions of the dataand instructions can be obtained dynamically, just in time, when neededfor execution. Thus, it is not required that the data and instructionsbe on a machine readable medium in entirety at a particular instance oftime.

Examples of computer-readable media include but are not limited torecordable and non-recordable type media such as volatile andnon-volatile memory devices, read only memory (ROM), random accessmemory (RAM), flash memory devices, floppy and other removable disks,magnetic disk storage media, optical storage media (e.g., Compact DiskRead-Only Memory (CD ROMS), Digital Versatile Disks (DVDs), etc.), amongothers. The instructions may be embodied in digital and analogcommunication links for electrical, optical, acoustical or other formsof propagated signals, such as carrier waves, infrared signals, digitalsignals, etc.

In general, a machine readable medium includes any mechanism thatprovides (i.e., stores and/or transmits) information in a formaccessible by a machine (e.g., a computer, network device, personaldigital assistant, manufacturing tool, any device with a set of one ormore processors, etc.).

In various embodiments, hardwired circuitry may be used in combinationwith software instructions to implement the techniques. Thus, thetechniques are neither limited to any specific combination of hardwarecircuitry and software nor to any particular source for the instructionsexecuted by the data processing system.

Although some of the drawings illustrate a number of operations in aparticular order, operations which are not order dependent may bereordered and other operations may be combined or broken out. While somereordering or other groupings are specifically mentioned, others will beapparent to those of ordinary skill in the art and so do not present anexhaustive list of alternatives. Moreover, it should be recognized thatthe stages could be implemented in hardware, firmware, software or anycombination thereof.

In the foregoing specification, the disclosure has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications may be made thereto without departing fromthe broader spirit and scope as set forth in the following claims. Thespecification and drawings are, accordingly, to be regarded in anillustrative sense rather than a restrictive sense.

What is claimed is:
 1. A device, comprising: an antenna to receive radiofrequency signals; a receiver; a diode coupled between the antenna andthe receiver; and a circuit coupled to the diode, the circuit forwardbiasing the diode to provide a path for the radio frequency signalsreceived by the antenna to reach the receiver and reverse biasing thediode to prevent the radio frequency signals received by the antennafrom reaching the receiver.
 2. The device of claim 1, wherein thecircuit is configured to change a state of the antenna according to datato be transmitted.
 3. The device of claim 2, wherein the circuitcomprises a current controller configured to selectively provide aforward bias current and change the state of the antenna.
 4. The deviceof claim 3, wherein the current controller comprises a transistorcoupled between the diode and ground; the transistor has a gate; whenthe gate is at a first voltage, the transistor provides the forward biascurrent to the diode; when the gate is at a second voltage, thetransistor stops the forward bias current.
 5. The device of claim 4,wherein the gate is configured to change an impedance between theantenna and the ground according to the data to be transmitted to changebackscattering of the antenna.
 6. The device of claim 4, wherein thetransistor is configured to alternate, according to the data to betransmitted, between connecting the antenna to the ground anddisconnecting the antenna from the ground.
 7. The device of claim 2,wherein the antenna has a plurality of feed points for the receiver; andthe diode is coupled to one of the plurality of feed points for thereceiver; and the device further comprises: a second diode coupledbetween the receiver and a second feed point of the plurality of feedpoints; and a second circuit coupled to the second diode to selectivelyforward bias and reverse bias the second diode.
 8. The device of claim1, wherein the circuit is configured to selectively connect anddisconnect the antenna to transmit data.
 9. The device of claim 1,wherein the circuit is further configured to selectively connect theantenna to ground and disconnect the antenna from the ground to transmitdata via the antenna.
 10. A device, comprising: a receiver; a pluralityof antennas; a plurality of diodes coupled between the receiver and theplurality of antennas respectively; and at least one controller coupledto the plurality of diodes, the at least controller configured to:forward bias one or more of the diodes to allow radio frequency signalsreceived via respective one or more of the antennas to reach thereceiver, and ground one or more of the antennas to transmit data. 11.The device of claim 10, wherein the at least one controller comprises aplurality of transistors; wherein gates of the transistors arecontrollable to selectively forward bias the diodes and to selectivelyground the antennas to modulate backscatter by the antennas.
 12. Thedevice of claim 10, wherein the at least one controller comprises aplurality of current controllers coupled to the plurality of diodesrespectively.
 13. The device of claim 12, wherein the plurality ofantennas comprise: a conductive patch having a plurality of feed points;a ground element; and a dielectric layer coupled between the conductivepatch and the ground element; wherein the diodes are coupled to the feedpoints.
 14. The device of claim 13, wherein the diodes are mounted invicinity of the feed points to which the diodes are connected.
 15. Adevice, comprising: a plurality of antennas; a receiver; a plurality ofdiodes coupled between the receiver and the plurality of antennasrespectively, wherein when forward biased each of the plurality ofdiodes provides a path for radio frequency signals from a respective oneof the plurality of antennas to reach the receiver; and at least onecontroller coupled to the plurality of diodes, wherein when in areceiving mode, the at least one controller forward biases at least oneof the diodes, and when in a transmitting mode, the at least onecontroller controls the diodes to change a backscatter state of at leastone of the antennas to transmit data.
 16. The device of claim 15,wherein the at least one controller comprises a plurality of transistorscoupled between the plurality of diodes and ground; when in thetransmitting mode, a gate of a transistor in the plurality oftransistors is controlled according to data being transmitted tomodulate radio frequency signals backscattered by a respective antennain the plurality of antennas; when in the receiving mode, the gate isapplied a voltage to forward bias a respective diode connected to therespective antenna.
 17. The device of claim 15, wherein the plurality ofantennas have different polarizations.
 18. The device of claim 15,wherein the at least one controller comprises a transistor coupledbetween the plurality of diodes and ground; when in the transmittingmode, a gate of the transistor is controlled according to data beingtransmitted to modulate backscattering by the antennas in parallel; whenin the receiving mode, the gate is applied a voltage to forward bias thediodes in parallel.
 19. The device of claim 15, wherein the plurality ofdiodes are mounted in vicinity of respective feed points to which thediodes are connected.
 20. The device of claim 15, wherein the receiverand the at least one controller are integrated on a single semiconductorsubstrate.